Health care burden as manifested by greater costs and utilization rises markedly with advancing age due in part to increasing prevalence of multiple chronic medical conditions (multimorbidity). However, current measures of multimorbidity explain only a modest proportion of the variation in subsequent costs. In order to constrain health care burden without negatively impacting health outcomes, improved understanding of key determinants of health care costs and utilization among older adults is essential. The overarching objective of this proposal is to construct interpretable, generalizable and validated models of health care costs and utilization among older community dwelling adults that incorporate measures of frailty, functional limitations and multimorbidity. We hypothesize that the potentially modifiable (but currently unmeasured) domains of the frailty phenotype and functional limitations are each associated with subsequent total and outpatient health care costs and inpatient and post-acute care utilization, after accounting for each other and multimorbidity. We will also evaluate associations of the deficit accumulation index (an omnibus measure designed to capture multiple age-related deficits) and individual frailty components and functional limitations with these outcomes. We will leverage comprehensive data from three prospective cohorts of community-dwelling older women and men (Study of Osteoporotic Fractures [SOF]; Health, Aging and Body Composition Study [Health ABC]; and Osteoporotic Fractures in Men Study [MrOS]) to characterize individual participant characteristics including the frailty phenotype and functional limitations using in-person exam data from 2002-2009 among 4,656 participants enrolled in a Medicare Fee-For-Service (FFS) plan. We will link these cohort data to individual participant claims-based measures of prevalent multimorbidity and incident health care costs and utilization. Finally, we will determine if findings from the pooled analyses of the three cohorts can be replicated in a large nationally representative sample of 5,579 community-dwelling Medicare FFS participants aged 65 years and older in the National Health and Aging Trends Study (NHATS) linked with their claims data. Our application is consistent with the NIA mission to conduct biological, clinical, behavioral, social, and economic research related to the diseases and conditions associated with the aging process. Our study implements concepts of the NIH Precision Medicine Initiative combining a wide range of data from four large epidemiologic studies leveraging the value of these cohorts in an efficient manner. In addition, our project is in line with the emerging concept of patient-centered outcomes, moving beyond the traditional medical model. Study findings will substantially improve the identification and characterization of older community-dwelling adults likely to require intense, costly health care; benefit health care systems/payers estimating costs vs. benefits of interventions directed at reducing progression to frailty and disability; and inform the design of future targeted intervention trials aimed at reducing health care costs and utilization among the aged population.